# SimpleITK 2.5.5 Release

**URL:** https://discourse.itk.org/t/simpleitk-2-5-5-release/7765
**Category:** Announcements
**Tags:** python, r, simpleitk
**Created:** [May 14, 2026, 6:10pm UTC](https://discourse.itk.org/t/simpleitk-2-5-5-release/7765 "2026-05-14T18:10:51Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![blowekamp](https://discourse.itk.org/user_avatar/discourse.itk.org/blowekamp/32/79_2.png) [@blowekamp](https://discourse.itk.org/u/blowekamp)
#### Post date: [May 14, 2026, 6:10pm UTC](https://discourse.itk.org/t/simpleitk-2-5-5-release/7765/1 "2026-05-14T18:10:51Z")

</div>

Announcing the SimpleITK 2.5.5 Release!

# Release Highlights

- 
## SimpleITK in R on the Windows operating system is available!

SimpleITK 2.5.5 is the first official release to support building SimpleITK with R wrapping for all major operating systems. It is recommended to use the [SimpleITKRInstaller](https://github.com/SimpleITK/SimpleITKRInstaller) to configure standard or custom builds without explicitly cloning the source code repository. Alternatively, R packages can be [built from the SimpleITK source code directly](https://simpleitk.readthedocs.io/en/latest/building.html) by turning the WRAP\_R flag on in the CMake configuration and following the [R-specific installation instructions](https://simpleitk.readthedocs.io/en/latest/building.html#r-installation).

- 
## Added Support for R 4.6.0
- 
## Added Python Wheels for Free-Threaded CPython 3.14

In the ABI section of the wheel filename, the `t` in `cp314t` indicates support for free-threading.

The small `t` in the wheel filename is a significant change. The Global Interpreter Lock (GIL) is now optional in CPython ([PEP 703](https://peps.python.org/pep-0703/)). With this change, Python natively supports true multithreading, running threads in parallel on multi-core systems and not in a serial fashion managed by the GIL. Read more about [free-threaded Python on python.org](https://docs.python.org/3/howto/free-threading-python.html). While this change may affect your native Python code, and requires a compatible SimpleITK built wheel, the other wheels continue to unlock the GIL during ITK code execution for parallel processing.

- 
## ITK 5.4.6

This distribution is based on the Insight Toolkit 5.4.6 release. Please see the [ITK release notes](https://docs.itk.org/en/release/releases/5.4.6.html) for details.

## Installing SimpleITK

Complete instructions on getting started with SimpleITK including downloading binaries or building SimpleITK can be found on the SimpleITK [Read the Docs web page](https://simpleitk.readthedocs.io/en/master/index.html).

**What’s Changed**

- ENH: Add free-threaded Python (3.14t) packaging support - for release by @blowekamp in [ENH: Add free-threaded Python (3.14t) packaging support - for release by blowekamp · Pull Request #2580 · SimpleITK/SimpleITK · GitHub](https://github.com/SimpleITK/SimpleITK/pull/2580)

- ENH: Update macOS CI runner from macos-13 to macos-14 by @blowekamp in [ENH: Update macOS CI runner from macos-13 to macos-14 by blowekamp · Pull Request #2584 · SimpleITK/SimpleITK · GitHub](https://github.com/SimpleITK/SimpleITK/pull/2584)

- Fix R CLOENV - for release and master by @blowekamp in [Fix R CLOENV - for release and master by blowekamp · Pull Request #2585 · SimpleITK/SimpleITK · GitHub](https://github.com/SimpleITK/SimpleITK/pull/2585)

- BUG: Patch SWIG superbuild for R 4.6.0 API removals by @blowekamp in [BUG: Patch SWIG superbuild for R 4.6.0 API removals by blowekamp · Pull Request #2587 · SimpleITK/SimpleITK · GitHub](https://github.com/SimpleITK/SimpleITK/pull/2587)

**Full Changelog** : [Comparing v2.5.3...v2.5.5 · SimpleITK/SimpleITK · GitHub](https://github.com/SimpleITK/SimpleITK/compare/v2.5.3...v2.5.5)